A transmission is used to match the speed and torque of a rotating load with that of the motor or engine driving it. The driven end is designated as the input while the shaft or member attached to the load is designated as the output.
In vehicular applications, the input speed is always higher than the output speed of a transmission, while in some industrial applications where high speed is required for an operation, the opposite is sometimes true. In any case, a transmission has an input and an output and has control over the ratio of rotational speed between them.
Gears have traditionally been used to achieve these speed ratios. Multiple gear sets are used within a transmission if a variety of fixed ratios is required. A more desirable device would offer the user the ability to continuously vary the speed ratio between input and output over a wide range. Continuously variable transmissions (CVT's) have been designed to achieve this result.
A wide variety of geometric alternatives and driving members have been tried over the years. Disk/disk, ball drives and belt drives have been used in CVT's. Some designs used sliding friction while others used rolling friction between members to transmit torque from input to output. While gears use mechanical interlocking to prevent slippage, friction drive elements are subject to slippage and may have a limiting capability to transfer torque. Therefore, the size of the elements themselves must be increased or the contact forces between them must be increased (or both) to provide adequate torque capability. The measures to prevent slippage work against the dual goals of achieving compactness and low component wear. This has been the principle impediment to the broad application of CVT's in heavy-duty applications.
Further, in the employment of gear systems for CVT applications, there exists a problem of continuously phasing the gear teeth of the gear in communication with the input shaft and the gear teeth in communication with the output shaft. The current invention provides a means for compensating for a continuously varying phase difference in a manner which is smooth and minimizes wear.